Technology to detect minute quantities of nucleic acids has advanced rapidly over the last two decades including the development of highly sophisticated amplification techniques such as polymerase chain reaction (PCR). Researchers have readily recognized the value of such technology to detect nucleic acids which are indicative of diseases and genetic features in human or animal test specimens. The use of probes and primers in such technology is based upon the concept of complementarity, that is, the bonding of two strands of a nucleic acid by hydrogen bonds between complementary nucleotides (also known as nucleotide pairs).
PCR is a significant advance in the art to allow detection of very small concentrations of a targeted nucleic acid. The details of PCR are described, for example, in U.S. Pat. No. 4,683,195 (Mullis et al), U.S. Pat. No. 4,683,202 (Mullis) and U.S. Pat. No. 4,965,188 (Mullis et al), although there is a rapidly expanding volume of literature in this field.
In order to effectively amplify and detect a target nucleic acid, it is usually necessary to isolate that nucleic acid from cellular and other specimen debris. Various lysing procedures are known, including freezing, treatment with digesting enzyme such as proteases (for example, Proteinase K), boiling, and use of various detergents (see for example U.S. Ser. No. 178,202, filed Apr. 6, 1988 by Higuchi, and EP-A-0 428 197, published May 22, 1991), solvent precipitations and heating protocols.
Once nucleic acids are extracted from cells or virus particles, however, there remains a need to separate them from other materials in the lysate in a simple and cost effective manner. One material known to complex with nucleic acids is polyethyleneimine and various chemical derivatives. It has been used to precipitate nucleic acids as contaminants in processes for isolating enzymes, and in affinity columns for capturing nucleic acids.
More recently, our colleagues have used polyethyleneimine in combination with an anionic phosphate ester surfactant to capture and selectively isolate nucleic acids. While this technique has been used with some success, it requires the use of two separate reagents in different steps in carefully controlled amounts. That is, the amount of phosphate ester surfactant used is dependent upon the amount of polyethyleneimine which is present in the precipitate with the nucleic acids. An improvement has been sought to reduce the number of steps and reagents needed for capture and isolation of nucleic acids.